Question 20 on magnesium reaction with water

Magnesium reacts in hot water to produce magnesium hydroxide and hydrogen gas, which turns red when exposed to phenolphthalein due to its alkaline nature. Why does it become colorless after a while?

There could be two reasons:

1) The chromogenic phenolphthalein is due to the reaction of triphenyl methyl alcohol ester with alkali to form a quinone planar structure, and the substances containing phenolic hydroxyl groups are easily oxidized, and the dissolved oxygen in the solution is oxidized and faded.

2) Because magnesium hydroxide is very unstable, it decomposes into colorless magnesium oxide and water.

It is recommended that you do a ** experiment: take a small amount of the faded solution, divide it into two test tubes, and then add phenolphthalein test solution or magnesium and hot water reaction mixture dropwise respectively, and observe the color change of the solution.

After adding phenolphthalein test solution dropwise to the fading solution, it turns red, and the cause of the problem is (1) above, and it does not change red, and the cause of the problem is (2) above

After fading, the mixture of magnesium and hot water reaction reaction is added dropwise in the solution, and it turns red, and the cause of the problem is (2) above, and it does not turn red, and the cause of the problem is (1) above

The experiment is very simple, and you can actually do it in the laboratory.

Magnesium hydroxide is a medium-strong alkali, which is usually relatively stable, and will only decompose when the solid is fired at high temperature, and will not decompose in aqueous solution.

Magnesium hydroxide is unstable and easily decomposes into magnesium oxide and water, which is the reason for color recovery.

The chemical formula of magnesium reaction with water is: mg+2h2o==mg(oh)2+h2.

Magnesium and water react, but the reaction between magnesium and water at room temperature is very slow, and the speed will increase if it is placed in hot water, but the resulting magnesium hydroxide will cover the surface of the magnesium metal, preventing the reaction from proceeding.

Magnesium has strong reducibility, can react with boiling water to release hydrogen, can produce dazzling white light when burning, magnesium and fluoride, hydrofluoric acid and chromic acid do not react, nor are they attacked by caustic alkali, but it is easily soluble in organic and inorganic acids.

Magnesium can be combined directly with nitrogen, sulfur and halogens, and organic chemicals including hydrocarbons, aldehydes, alcohols, phenols, amines, lipids and most oils have little or no effect on magnesium.

However, the reaction with halogenated hydrocarbons in the absence of water is more violent (the generation of Grignard reagent) magnesium can react with carbon dioxide, so magnesium combustion cannot be extinguished with carbon dioxide fire extinguishers. Because magnesium can react with N2 and O2, when magnesium is burned in the air, it burns violently and emits dazzling white light, which is exothermic and produces a white solid.

In vinegar, bubbles emerge quickly, float on the vinegar surface, and gradually disappear. Some fireworks and flares contain magnesium powder, which takes advantage of the dazzling white light that magnesium emits when burned in the air. The valency of magnesium in chemical reactions is usually +2 valence.

The above content reference: Encyclopedia - Magnesium.

The reaction between magnesium and water is mainly to produce magnesium hydroxide, and then magnesium hydroxide is a white substance precipitate, and at the same time it will produce a colorless gas, which is hydrogen.

The reaction equation of magnesium and water: mg+2h2o=mg(oh)2+h2(gas).

Magnesium belongs to the second main group of elements, which is in the same period as sodium, so the metallicity is weaker than sodium, and the reaction products with water are similar to the reaction with sodium and water, and the conditions are higher than those of sodium.

Detailed explanation:Magnesium oxide is a compound composed of pure ionic bonds, while magnesium hydroxide is an ionic compound mixed with covalent bonds, that is, hydrogen and oxygen need to share electron pairs to form the outermost 7-electron structure, and then use magnesium to transfer the 2 electrons to the two hydroxide groups to form the outermost 8-electron structure, and finally form a stable compound.

The above content reference: Encyclopedia - hydrogen rod.

<>1. Magnesium and cold water will react very slowly.

2. Magnesium and hot water above 80 will react faster, and the phenomenon of gas production can be seen.

3. Magnesium reacts with high-temperature water vapor to form magnesium oxide and hydrogen, and magnesium hydroxide is a decomposition product at high temperature.

Magnesium and water react very slowly at room temperature, and the reaction rate increases in hot water, but the resulting magnesium hydroxide will cover the surface of the magnesium metal and prevent the reaction from proceeding.

The equation for the reaction of magnesium and water is mg+2h2o=mg(oh)2+h2(gas) (condition: heating).

According to the table of metal activity sequence, the reaction equation for metals before Mg (including Mg) is written in the same way as H2O. The metal behind mg cannot react directly with water under general conditions, and aluminum needs to react with water in the presence of a strong base.

Properties of magnesiumMagnesium has strong reducibility, can react with boiling water to release hydrogen, can produce dazzling white light when burning, magnesium and fluoride, hydrofluoric acid and chromic acid do not react, and are not subject to caustic erosion, but it is easily soluble in organic and inorganic acids, magnesium can be directly combined with nitrogen, sulfur and halogens, including hydrocarbons, aldehydes, alcohols, phenols, amines, lipids and most oils, including organic chemicals and magnesium only slightly or not at all.

The above content reference: Encyclopedia - Magnesium.

Magnesium reacts directly with water to form hydrogen and magnesium hydroxide.

Because magnesium is very active, it reacts with oxygen when exposed to air to form magnesium oxide, which is a dense oxide layer that prevents oxygen from reacting with magnesium in the inner bright mold. Therefore, the oxide layer should be wiped off before magnesium seepage is put into the water, and the water must be heated.

mg can react in cold water, but it only reacts very slowly, if you look carefully, you can indeed see that the bubble bond is good. Heating speeds up the rate of reaction. mg+2h20=mg(oh)2+h2↑。

In 1808, David of England used potassium to reduce magnesium oxide to make magnesium metal. It is a silvery-white light alkaline earth metal with active chemical properties, which can react with acid to form hydrogen, and has certain ductility and heat dissipation. Magnesium is widely distributed in nature and is one of the essential elements for the human body.

1. Magnesium reacts very slowly with cold water.

2. Magnesium and hot water above 80 will react quickly, and you can see the obvious phenomenon of gas production.

3. Magnesium reacts with high-temperature water vapor to form orange precursor magnesium oxide and hydrogen, which is a decomposition product at high temperature.

Magnesium and water react very slowly at room temperature and the reaction rate increases in hot water, but the resulting magnesium hydroxide coats the surface of the magnesium metal and prevents the reaction from proceeding.